/**
 * Copyright 1996 self.com.au
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License. (http://www.apache.org/licenses/LICENSE-2.0)
 *
 * Unless required by applicable law or agreed to in writing, software distributed under the License is distributed 
 * on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for 
 * the specific language governing permissions and limitations under the License.
 *
 * <dhamma-message src="Atisha (11th century Tibetan Buddhist master)">
 * 	The greatest achievement is selflessness. The greatest worth is self-mastery.
 * 	The greatest quality is seeking to serve others. The greatest precept is continual awareness.
 * 	The greatest medicine is the emptiness of everything. The greatest action is not conforming with the worlds ways.
 * 	The greatest magic is transmuting the passions. The greatest generosity is non-attachment.
 * 	The greatest goodness is a peaceful mind. The greatest patience is humility.
 * 	The greatest effort is not concerned with results. The greatest meditation is a mind that lets go.
 * 	The greatest wisdom is seeing through appearances. 
 * </dhamma-message>
 *
 * @author Ashin Wimalajeewa
 *
 * Note, this is a very old runtime library that I have evolved since 1996. I rarely use it
 * now because the Apache Commons project has made it obsolete.
 */
package self.math;

public class LinearEquation {
  private boolean isXOnly = false;
  public  double m , c;
  
  public LinearEquation() {
	// nothing to do.
  }
  
  public LinearEquation( double m, double c ) {
    setCoefficients( m, c );
  }
  
  public LinearEquation( double x1, double y1, double x2, double y2 ) {
    setBasedOnPoints( x1, y1, x2, y2 );
  }
  
  public void setCoefficients( double m, double c ) {
//    if ( double.isInfinite(m) || double.isNaN(c) )
//      isXOnly = true;
    isXOnly =  ( ( Double.isInfinite(m) || Double.isNaN(c) ) );
    this.m = m;
    this.c = c;
  }
  
  public void setBasedOnPoints( double x1, double y1, double x2, double y2 ) {
    m = ( y2 - y1 ) / (x2 - x1);
    c = y1 - (m * x1);
    isXOnly =  ( ( Double.isInfinite(m) || Double.isNaN(c) ) );
    if ( isXOnly ) 
      c = x2;
  }
  
  public boolean getIntersectingPoints( LinearEquation line, double[] xyPoint ) {
    if ( isXOnlyEquation() && line.isXOnlyEquation() )  // parallel lines
      return false;
    if ( m == 0 && line.m == 0 )                        // parallel lines
      return false;
    if ( isXOnlyEquation() ) {
      xyPoint[0] = c;
      xyPoint[1] = line.solveForX( xyPoint[0] );
    } else if ( line.isXOnlyEquation() ) {
      xyPoint[0] = line.c;
      xyPoint[1] = solveForX( xyPoint[0] );
    } else {
      xyPoint[0] = (line.c - c) / (m - line.m);
      xyPoint[1] = solveForX( xyPoint[0] );
    }
    return true;
  }
  
  public void getPerpendicular( LinearEquation perp, int xVal, int yVal ) {
    double perpM = isXOnly ? 0: -( 1/ m );
//    double perpM = isXOnly ? 0: ( m == 0? 0: -( 1/ m ));
    double perpC = Double.isInfinite(perpM)? xVal: (yVal - (perpM*xVal));
    perp.setCoefficients( perpM, perpC );
  }
  
  public double solveForX( double xVal ) {
    if ( isXOnly )
      throw new IllegalStateException( "Equation in the form x=" + c );
    return (m*xVal) + c;
  }
  
  public double solveForY( double yVal ) {
    if ( isXOnly )
      return c;
    else
      return (yVal -c)/m;
  }
  
  public boolean isXOnlyEquation() {
    return isXOnly;
  }
    
  public String toString() {
    return "[m=" + m + ", c=" + c + ", isXOnly=" + isXOnly + "]";
  }
}